1. Field of the Invention
The present invention relates to infrared sensors, in particular, to a thermopile-type infrared sensor.
2. Description of the Related Art
A known thermopile type infrared sensor is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 63-318175. This infrared sensor is provided with a temperature-sensing resistor film at a corner of a substrate, for measuring and compensating for temperature of the cold junction of a thermopile so as to improve the accuracy of the infrared sensor. The temperature-sensing resistor film is made of a material such as bismuth (Bi) or antimony (Sb) which is the same thermoelectric material as used in thermocouples.
However, since Bi or Sb is a low-melting-point semimetal, it is difficult to perform deposition of the temperature-sensing resistor film without variations in the properties of the films between products. Variations over time due to moisture absorption and heat history are significant; therefore, Bi or Sb is not ideal as a material for a resistor film for temperature compensation. Moreover, since a Bi or Sb film does not adhere well to a substrate, another material must be used for an electrode for extracting sensor signals.
Accordingly, it is an object of the present invention to provide an infrared sensor having superior sensitivity which is provided with a temperature-compensation resistor film which has high reproducibility, the quality of which is not significantly deteriorated over time.
According to the present invention, a thermopile-type infrared sensor comprises a thermocouple made of thermoelectric materials which are different from each other, the thermoelectric materials being connected to each other by a bonding material which is different from the thermoelectric materials, and a substrate provided with the thermopile formed thereon, wherein a temperature-compensation resistor film made of the same material as the bonding material is provided on the substrate.
The thermopile-type infrared sensor according to the present invention may further comprise electrodes for extracting sensor outputs, which are made of the same material as the bonding material.
The bonding material may include one material selected from the group consisting of platinum, tungsten, palladium, nickel, and chromium.
By using a bonding material, which differs from the thermoelectric materials forming the thermocouple of the thermopile in the infrared sensor, for junctions between the thermoelectric materials, the quality of the electrical junction can be improved, and diffusion or the like of the materials can be avoided. By using the bonding material for the temperature-compensation resistor film, the junctions of the thermocouple and the temperature-compensation resistor film can be made simultaneously without additional processes which are required in the known method. The deposition of a film can be easily performed by using the bonding material which is not likely to vary in quality over time, whereby the accuracy in compensation for temperature is improved and an infrared sensor having superior sensitivity is obtainable by using the temperature-compensation resistor film formed by the bonding material.
According to the present invention, the temperature of cold junctions of a thermopile can be stably and accurately measured, whereby a thermopile infrared sensor having superior sensitivity can be provided at low manufacturing costs.
The above object, further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawing.